Map construction has in recent years gained considerable prominence in molecular biology. This is especially true in organisms with large genomes where comprehensive maps are essential for both broad, genome-wide efforts, such as the Human genome Project, as well as focused efforts of gene identification. Current work is severely hindered by the lack of a chromosome-specific large-insert library. One obvious problem is that the Y is always half as abundant as all other autosomes. In collaboration with Drs. Bruce Lahn and David Page, we plan to flow-sort sufficient human Y chromosomes to construct a human Y-specific BAC library. Using about 1 fg of flow -sorted Y chromosomes, the material will be partially digested, size selected at 100kb and greater DNA fragments to ligate into BAC vectors. After transformation, in excess of 3000 clones will be picked to achieve a >5 fold coverage of the human Y. This BAC library would then be used for the construction of a fine-scale map of the Y chromosome, as well as a number of other pursuits, including the identification of genes with regions of interest.